Nitrogen dioxide (NO2) is a reactive gas formed as a result of combustion processes, most notably those that result in tobacco smoke and home gas stove emissions. Children exposed to indoor NO2 originating from secondary tobacco smoke or home gas stoves represent a significant health problem. Airway epithelium is a major target of NO2 toxicity. Studies have reported that exposure of human adult volunteers to low concentrations of NO2 led to clinically significant increases in airway reactivity. The mechanism of airway sensitization in response to NO2 exposure remains unknown. The central hypothesis of this application is that lipid peroxidation products generated from the interaction of NO2 with airway epithelium mediate the toxicity of this reactive gas and that specific peroxidation product(s) are responsible for increasing epithelial reactivity to stimuli. The goals of these studies are: (1) to identify and quantitate lipid peroxidation products generated through either enzymatic pathways (i.e., cyclooxygenase or lipoxygenase) or nonenzymatic pathways (i.e., those resulting in alpha, Beta-unsaturated aldehydes); (2) to examine the effects the effects of NO2 or NO2-induced peroxidation products on epithelial mucin secretion, permeability, and ion transport; and (3) to assess alterations of epithelial reactivity resulting from exposure to either NO2 or peroxidation products through treatment with stimuli, histamine or methacholine. Generation of peroxidation products will be temporally related to changes of airway secretion, permeability, and ion transport and altered cellular reactivity. Alterations in the profile of peroxidation products in response to treatment with antioxidants and inhibitors of arachidonate metabolism will be correlated with changes in airway function and reactivity. Most of these studies will utilize in vitro tracheobronchial epithelial cultures, which form a mucociliary layer that is almost identical to that observed in vivo. NO2-induced peroxidation products identified and quantified from in vitro exposure of airway epithelium will be correlated with peroxidation products generated from airway epithelium in response to in vivo exposure to assess their potential relevance. We expect that lipid peroxidation products generated from the interaction of NO2 with airway epithelium mediate many of the toxic effects of this reactive gas. Specific peroxidation products may alter epithelial function and reactivity. Identification of peroxidation products formed in response to in vitro and in vivo exposure to NO2 will provide information on the mechanism of action of NO2 and which products are responsible for increasing airway reactivity.